Arteriosclerosis has long been a serious cardiovascular problem, involving the accumulation of deposits or plaque on the interior walls of blood vessels, primarily arteries. Accumulation of such plaque can result in areas of the blood vessel in which a significant portion of the flow is blocked. Such significant blockage is characterized as a stenosis, which causes reduced flow through the blood vessel.
In the past, serious stenoses could generally be alleviated only by bypassing of the blood vessel. More recently, angioplasty techniques were developed to open stenoses in arteries. In such techniques, a balloon catheter is typically inserted in the blood vessel, and the balloon is positioned at the site of the stenosis. Upon inflation, the balloon presses radially on deposited plaque at the site and on the blood vessel wall behind the plaque. Plaque deposits are often irregular in transverse cross-section. Thick portions interfere with the uniform expansion of the balloon, and are, in their composition, non-uniform. These considerations increase the possibility of damage to the artery walls. It has previously been suggested to use a guide wire outside of and parallel to a catheter balloon to produce a crack in heavily calcified plaque, giving improved results and larger openings with less pressure and damage. Such techniques were previously used when normal balloon pressure did not satisfactorily dilate the vessel.
Still other techniques for improving angioplasty treatment include the suggestion of longitudinal cutting strips fastened on the balloon wall. Expansion of the balloon forces these edges outward radially to cut into the plaque. Such cutting edges seriously reduce the flexibility of the balloon, and increase the crossing profile. These features impose limitations on the ability to position the device in tortuous vessels.
Still other improvements in angioplasty techniques involved the balloon itself, providing balloons with improved burst pressure and strength characteristics balanced such that a balloon, if failure occurred, would burst in the longitudinal or axial direction as opposed to the transverse direction, facilitating removal under such circumstances.
A continuing need exists for angioplasty apparatus and techniques that balance the effective opening of the stenosis, minimal damage to the wall of the blood vessel, and minimization of the reformation of the stenosis after completion of the angioplasty.